Added support for skipping redundant dart2js compilations.

tools/testing/dart/test_progress.dart

Index: tools/testing/dart/test_progress.dart
diff --git a/tools/testing/dart/test_progress.dart b/tools/testing/dart/test_progress.dart
index 33e0765cbd4d471415da61f602066577b0be1dce..95aa8a46dc7cf657568abc45b38e96b5dbcb09fd 100644
--- a/tools/testing/dart/test_progress.dart
+++ b/tools/testing/dart/test_progress.dart
@@ -53,6 +53,10 @@ class ProgressIndicator {
       }
       _appendToFlakyFile(buf.toString());
     }
+    for (var commandOutput in test.commandOutputs.values) {
+      if (commandOutput.compilationSkipped)
+        _skippedCompilations++;
+    }
 
     if (test.lastCommandOutput.unexpectedOutput) {
       _failedTests++;
@@ -71,6 +75,13 @@ class ProgressIndicator {
     _allTestsKnown = true;
   }
 
+  void _printSkippedCompilationInfo() {
+    if (_skippedCompilations > 0) {
+      print('\n$_skippedCompilations compilations were skipped because '
+            'the previous output was already up to date\n');
+    }
+  }
+
   void _printTimingInformation() {
     if (_printTiming) {
       // TODO: We should take all the commands into account
@@ -93,6 +104,7 @@ class ProgressIndicator {
   void allDone() {
     _printFailureSummary();
     _printStatus();
+    _printSkippedCompilationInfo();
     _printTimingInformation();
     stdout.close();
     stderr.close();
@@ -225,6 +237,7 @@ class ProgressIndicator {
   int _foundTests = 0;
   int _passedTests = 0;
   int _failedTests = 0;
+  int _skippedCompilations = 0;
   bool _allTestsKnown = false;
   Date _startTime;
   bool _printTiming;
@@ -252,6 +265,7 @@ abstract class CompactIndicator extends ProgressIndicator {
   void allDone() {
     stdout.write('\n'.charCodes);
     _printFailureSummary();
+    _printSkippedCompilationInfo();
     _printTimingInformation();
     if (_failedTests > 0) {
       // We may have printed many failure logs, so reprint the summary data.